A diesel engine may include a selective catalytic reduction (SCR) catalyst to convert NOx to N2, H2O, and CO2. The diesel engine may also include a particulate filter to trap carbonaceous soot. The may be stored until the particulate filter is filled, then the soot may be combusted to regenerate the particulate filter. The particulate filter may be regenerated by heating exhaust gases in an oxidation catalyst and supplying the heated exhaust gases to the particulate filter where the heated exhaust gases may heat the soot until the soot begins to combust in an oxygen rich environment. However, the SCR is heated when the particulate filter is heated, and heating the SCR reduces the efficiency of the SCR. The SCR may remain above a desired temperature for a period of time even after the particulate filter is regenerated. Therefore, it may be desirable to provide a way of reducing an amount of time a SCR is at a temperature greater than a threshold temperature where SCR efficiency may be lower than a threshold.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: increasing turbocharger boost pressure via a controller while driver demand torque is substantially constant in response to ceasing regeneration of a particulate filter.
By increasing boost pressure in response to ceasing particulate filter regeneration while driver demand torque is substantially constant, it may be possible to cool a SCR after particulate filter regeneration so that SCR efficiency may be increased in a short amount of time. The boost pressure may be increased and a charge air cooler bypass valve may be closed to increase exhaust flow and reduce exhaust gas temperature, thereby cooling the SCR. The exhaust flow rate may be reduced to a first flow rate when SCR temperature is less than a first threshold, and the exhaust flow rate may be reduced to a second flow rate when the SCR temperature is less than a second threshold. The reduction of exhaust flow allows for SCR cooling while at the same time increasing engine efficiency.
The present description may provide several advantages. In particular, the approach may reduce engine emissions by increasing SCR efficiency in a reduced amount of time. In addition, the approach may allow for increased engine efficiency while still reducing SCR temperature. Further, the approach may be applicable to four stroke and two stroke diesel engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.